JP6896241B2 - Medical suture - Google Patents

Description

The present invention relates to medical sutures used in medical procedures such as surgery or treatment of injuries.

Traditionally, medical sutures used in medical procedures such as surgery or treatment of injuries have been used. In this medical suture, various resins are applied to the outer surface of the medical suture for the purpose of improving the operability of the suture, the slidability to the suture portion, or the slipperability (easiness of moving the knot when tying). The material is coated. For example, Patent Document 1 below discloses that coating a suture with 2-methacryloyloxyethyl phosphorylcholine (hereinafter referred to as "MPC") enhances the ease and retention of the suture when the surgeon ties the suture. ing.

Japanese Unexamined Patent Publication No. 2010-513678

However, in the suture described in Patent Document 1, when the suture wound in the packaging container in an annular shape and stored is taken out from the packaging container, the suture tends to have a curl and a curl. There was a problem that it was difficult to solve.

The present invention has been made to address the above problems, and an object of the present invention is to provide a medical suture that is hard to have a curl or can easily eliminate the curl.

In order to achieve the above object, the feature of the present invention is a medical suture in which one thread is composed of one or more fibrous ultrafine threads, and the ultrafine thread is 2-methacryloyloxy on the outer surface. A cover layer made of ethylphosphorylcholine (MPC) is formed, and the cover layer has a weight of 0.05% or more and less than 0.3% of the total weight of the wire rod forming the ultrafine yarn and forming the cover layer. In addition, it is formed in a state where a part of the outer surface of the wire rod is exposed and covers 50% or more of the surface surface of the wire rod with uniform formation densities in the axial direction and the circumferential direction of the wire rod .

According to the characteristics of the present invention configured in this way, in the medical suture, the cover layer made of 2-methacryloyloxyethyl phosphorylcholine (MPC) is 0.05% or more of the total weight of the wire rod constituting the ultrafine yarn and is 0. According to the experiment of the present inventor, the medical treatment which is housed in a ring in a packaging container while improving the operability of suturing, the slidability to the sutured portion or the slipperability by being formed by a weight of less than 3%. It was confirmed that the suture was difficult to curl or the curl was easily eliminated.

Further, according to the feature of the present invention configured as described above, since the medical suture is formed in a state where the cover layer is partially exposed on the outer surface of the wire rod, it covers the entire outer surface of the wire rod. It is not necessary to form the cover layer, the amount of MPC used and the work load for forming the cover layer can be reduced, and the cover layer can be formed efficiently.

Further, according to the feature of the present invention configured as described above, the medical suture is formed in a state where the cover layer covers 50% or more of the surface area of the wire rod with uniform formation densities in the axial direction and the circumferential direction of the wire rod. Therefore, it is possible to reduce the amount of MPC used and the work load for forming the cover layer while maintaining various characteristics such as operability, slidability, and slipperiness of the cover layer made of MPC, which is efficient. The cover layer can be formed.

In order to achieve the above object, the feature of the present invention is a medical suture in which one thread is composed of one or more fibrous ultrafine threads, and the ultrafine thread is 2-methacryloyloxy on the outer surface. A cover layer made of ethylphosphorylcholine (MPC) is formed, and the cover layer has a weight of 0.05% or more and less than 0.3% of the total weight of the wire rod forming the ultrafine yarn and forming the cover layer. Moreover, it is formed in a state where the outer surface of the wire rod is completely covered.

According to the characteristics of the present invention configured in this way, in the medical suture, the cover layer made of 2-methacryloyloxyethyl phosphorylcholine (MPC) is 0.05% or more of the total weight of the wire rod constituting the ultrafine yarn and is 0. According to the experiment of the present inventor, the medical treatment which is housed in a ring in a packaging container while improving the operability of suturing, the slidability to the sutured portion or the slipperability by being formed by a weight of less than 3%. It was confirmed that the suture was difficult to curl or the curl was easily eliminated.

Another feature of the present invention is that in the medical suture, the cover layer is 0.1% or more and less than 0.3% of the total weight of the wire rod forming the cover layer by forming the ultrafine thread. It is formed by weight.

According to another feature of the present invention configured in this way, the medical suture is formed with a weight of 0.1% or more and less than 0.3% of the total weight of the wire rod whose cover layer constitutes the ultrafine thread. Therefore, the cover layer can be easily formed as compared with the case where the cover layer is formed with less than 0.1% of the total weight of the wire rod.

It is an exploded side view which showed the outline of the appearance structure and the internal structure of the medical suture which concerns on one Embodiment of this invention typically. FIG. 5 is an exploded side view schematically showing an outline of an external configuration and an internal configuration of the ultrafine yarn constituting the core yarn and the outer layer yarn in the medical suture shown in FIG. 1. It is a partially enlarged side view which shows the state of the cover layer partially formed on the outer surface of the ultrafine thread which constitutes the medical suture which concerns on the modification of this invention.

Hereinafter, an embodiment of the medical suture thread according to the present invention will be described with reference to the drawings. FIG. 1 is an exploded side view schematically showing an outline of an external configuration and an internal configuration of the medical suture 100 according to the present invention. It should be noted that each of the figures referred to in the present specification is schematically shown by exaggerating some of the components in order to facilitate the understanding of the present invention. Therefore, the dimensions and ratios between the components may be different. The medical suture 100 is an instrument for suturing a part of body tissue such as human or animal skin, muscle or organ.

(Structure of medical suture 100)
The medical suture 100 is mainly composed of a core thread 110 and an outer layer thread 120. The core thread 110 is a thread arranged inside the medical suture thread 100, and is composed of a set of a plurality of ultrafine threads 111. In the present embodiment, the core yarn 110 is formed by twisting two bundles composed of a set of a plurality of ultrafine yarns 111 into one yarn. As a result, the core thread 110 is formed to have a thickness of about 0.27 mm in the present embodiment.

As shown in FIG. 2, the ultrafine yarn 111 is the smallest unit yarn constituting the core yarn 110, and is composed of a wire rod 111a made of a resin material, a natural material, or a metal material. In this case, as the resin material, for example, nylon, polypropylene, polyester, polyvinylidene fluoride (polyvinylidene fluoride) or the like can be used. Further, as a natural material, Katogut (a thread made from the intestine of an animal) or silk thread can be used. Further, as the metal material, stainless steel, titanium, magnesium or the like can be used.

The thickness of the ultrafine thread 111 is variously formed according to the thickness of the medical suture thread 100, but is generally formed to be 1 μm or more and 1 mm or less. In the present embodiment, the ultrafine yarn 111 is composed of a polyester yarn having a thickness of about 10 μm.

An extension cover layer 112 is formed on the surface of the wire rod 111a in the ultrafine yarn 111. The extension cover layer 112 is a resin layer in which the outer surface of the wire rod 111a of the ultrafine yarn 111 is covered with MPC (2-methacryloyloxyethyl phosphorylcholine). In this case, the extension cover layer 112 may be composed of only MPC, but the extension cover layer 112 is configured so that MPC is contained as a main component having the highest content rate with respect to other components among the components of the extension cover layer 112. It suffices if it is done. In the present embodiment, the extension cover layer 112 is composed of only MPC.

Further, the extension cover layer 112 is preferably formed so as to completely cover the outer surface of the wire rod 111a, but the surface area of the wire rod 111a is 50 with substantially uniform formation densities in the axial direction and the circumferential direction of the wire rod 111a. It is preferable that it is formed so as to cover% or more (more preferably 80% or more). That is, as shown in FIG. 3, the extension cover layer 112 may be formed in a state where a part of the outer surface is exposed by being formed as spots on the outer surface of the wire rod 111a.

Here, the formation density substantially uniform in the axial direction and the circumferential direction of the wire rod 111a means that the portion where the outer surface of the wire rod 111a is exposed (the portion where the extension cover layer 112 is not formed) and the extension cover layer 112 are formed. The portions are substantially evenly arranged in the axial direction and the circumferential direction of the wire rod 111a. When the outer surface of the wire rod 111a is observed with a magnifying glass such as an electron microscope, the substantially uniform formation density is determined by the portion where the outer surface of the wire rod 111a is exposed and the portion where the extension cover layer 112 is formed. It suffices to appear to be evenly distributed, and does not necessarily have to be exactly even.

The extension cover layer 112 is formed on the outer surface of the wire rod 111a within a weight range of 0.05% or more and less than 0.3% of the total weight of the wire rod 111a. That is, the extension cover layer 112 is formed on the outer surface of the wire rod 111a within a weight range of 0.05% or more and less than 0.3% of the total weight of the wire rod 111a to cure the medical suture 100. Can be suppressed and flexibility can be maintained. In this case, the thickness of the extension cover layer 112 is set according to the use of the medical suture 100 or the preference of the user. In the present embodiment, the extension cover layer 112 is formed on the outer surface of the wire rod 111a with a weight of 0.1% of the total weight of the wire rod 111a.

The outer layer yarn 120 is a yarn arranged so as to cover the outer surface of the core yarn 110 described above, and is composed of a set of a plurality of ultrafine yarns 121. In the present embodiment, the outer layer yarn 120 is formed by knitting six bundles composed of a set of a plurality of ultrafine yarns 121 into one yarn. As a result, the outer layer yarn 120 is formed to have a thickness of about 0.6 mm in the present embodiment. That is, in the present embodiment, the medical suture 100 is formed to have a thickness of about 0.6 mm. The outer layer yarn 120 is formed in a state of completely covering the outer surface of the core yarn 110.

The ultrafine yarn 121 is the smallest unit yarn constituting the outer layer yarn 120, and is composed of a wire rod 121a made of a resin material, a natural material, or a metal material. In this case, as the resin material, for example, nylon, polypropylene, polyester, polyvinylidene fluoride (polyvinylidene fluoride) or the like can be used. Further, as a natural material, Katogut (a thread made from the intestine of an animal) or silk thread can be used. Further, as the metal material, stainless steel, titanium, magnesium or the like can be used.

The thickness of the ultrafine thread 121 is variously formed according to the thickness of the medical suture thread 100, but is generally formed to be 1 μm or more and 1 mm or less. In the present embodiment, the ultrafine yarn 121 is composed of a polyester yarn having a thickness of about 10 μm. That is, in the present embodiment, the ultrafine thread 121 is composed of exactly the same thread as the ultrafine thread 111. Since the ultrafine thread 121 is appropriately formed according to the specifications of the medical suture thread 100, it is natural that the ultrafine thread 121 may be made of a different material and / or a different wire diameter from the ultrafine thread 111.

As shown in FIG. 2, the extra-fine yarn 121 has an outer wire cover layer 122 formed on the surface of the wire rod 121a. The outer wire cover layer 122 is a resin layer in which the outer surface of the wire rod 121a is covered with MPC (2-methacryloyloxyethyl phosphorylcholine). In this case, the external line cover layer 122 may be composed of only MPC, but the external line cover layer 122 is configured so that MPC is contained as a main component having the highest content rate with respect to other components among the constituent components of the external line cover layer 122. It may have been done. Further, the outer line cover layer 122 may be composed of a resin material other than MPC or a synthetic resin containing a resin other than MPC as a main component. In the present embodiment, the outer line cover layer 122 is composed of only MPC.

Further, the outer wire cover layer 122 is preferably formed in a state of completely covering the outer surface of the wire rod 121a, but the surface area of the ultrafine yarn 121 has a substantially uniform formation density in the axial direction and the circumferential direction of the wire rod 121a, respectively. It is preferable that it is formed so as to cover 50% or more (more preferably 80% or more). That is, as shown in FIG. 3, the outer line cover layer 122 may be formed in a state where a part of the outer surface is exposed by being formed as spots on the outer surface of the wire rod 121a. Here, since the formation densities of the wire rod 121a that are substantially uniform in the axial direction and the circumferential direction are the same as those of the extension cover layer 112, the description thereof will be omitted.

The outer wire cover layer 122 is formed on the outer surface of the wire rod 121a within a weight range of 0.05% or more and less than 0.3% of the total weight of the wire rod 121a. That is, the outer wire cover layer 122 is formed on the outer surface of the wire rod 121a within a weight range of 0.05% or more and less than 0.3% of the total weight of the wire rod 121a, so that the medical suture 100 is flexible. You can get a sexual or smooth feel. In this case, the thickness of the outer line cover layer 122 is set according to the use of the medical suture 100 or the preference of the user. In the present embodiment, the outer wire cover layer 122 is formed on the outer surface of the wire rod 121a with a weight of 0.1% of the total weight of the wire rod 121a, similarly to the extension cover layer 112.

That is, in the present embodiment, the ultrafine thread 121 is configured to be exactly the same as the ultrafine thread 111. The extra-fine thread 121 may have an outer line cover layer 122 having a structure different from that of the extension cover layer 112, or the outer line cover layer 122 may be omitted. In FIG. 1, in order to facilitate understanding of the internal structure of the medical suture 100, one extrafine thread 111 and one extrafine thread 121 are extracted and shown, and the extension cover layer 112 and the outer line cover layer 122 are shown. The illustration is omitted. Further, in FIGS. 2 and 3, the ultrafine thread 111 and the ultrafine thread 121 are shown in one common diagram.

(Manufacturing of medical suture 100)
Next, the manufacturing process of the medical suture 100 will be described. A worker who manufactures the medical suture 100 first prepares an extra-fine thread 111 on which the extension cover layer 112 is not formed and an extra-fine thread 121 on which the outer line cover layer 122 is not formed. Specifically, the wire rods 111a and 121a, which are the bases of the ultrafine yarns 111 and 121, are prepared, respectively.

In this case, the wire rods 111a and 121a are manufactured by the conventional method for manufacturing sutures, respectively. Therefore, the operator may manufacture the wire rods 111a, 121a, which are the bases of the ultrafine yarns 111, 121, by himself / herself, but can purchase and obtain a commercially available wire rod. In the present embodiment, the operator prepares polyester wire rods 111a and 121a of size 11-0 (about 20 μm) (standards for sutures according to the Pharmaceutical Affairs Law), respectively.

Next, the operator forms the extension cover layer 112 and the outside line cover layer 122 with respect to the wire rods 111a and 121a, respectively. Specifically, the operator immerses the wire rods 111a and 121a in a solution containing MPC (for example, an ethanol solution) to form the extension cover layer 112 and the outer wire cover layer 122 on the surfaces of the wire rods 111a and 121a, respectively. be able to.

In this case, the operator holds the MPC in a state where a plurality of wire rods 111a and 121a are collected and bundled, a roll state in which the wire rods 111a and 121a are wound in a ring shape, or a state in which the wire rods 111a and 121a wound in a roll shape are pulled out linearly. Can be immersed in the containing solution. Further, the concentration of the solution containing MPC and the time for immersing the wire rods 111a and 121a are appropriately determined according to the thickness of the extension cover layer 112 and the outside line cover layer 122 to be formed.

Then, the operator performs a drying treatment and a sterilization treatment on the wire rods 111a and 121a pulled up from the solution containing MPC. As a result, the operator can obtain the extra-fine yarns 111 and 121 in which the extension cover layer 112 and the outside line cover layer 122 are formed on the outer surfaces of the wire rods 111a and 121a, respectively. The worker forms the extension cover layer 112 and the outer line cover layer 122 in spots on the surfaces of the wires 111a and 121a by applying vibration or setting the drying temperature high during drying of the wires 111a and 121a. be able to.

Next, the operator forms the core thread 110. Specifically, an operator twists two bundles of a plurality of ultrafine yarns 111 using a twisting machine (not shown) to form one core yarn 110. As a result, the operator can form the core yarn 110 to a thickness of about 0.27 mm in the present embodiment.

Next, the operator forms the outer layer yarn 120. Specifically, an operator uses a knitting machine (not shown) to knit five bundles of a plurality of ultrafine yarns 121 on the outside of the core yarn 110 to form one yarn. That is, the process of forming the outer layer thread 120 forms the medical suture thread 100 in which the core thread 110 is completely covered with the outer layer thread 120. The medical suture 100 is formed in the present embodiment with an outer diameter of about 0.6 mm.

Next, the operator can complete the medical suture 100 by obtaining a sterilization process, an inspection process, and a packaging process for the medical suture 100. In this case, the medical suture 100 is housed in a packaging container (not shown) in a state of being wound in an annular shape. Further, the medical suture 100 may be packaged in a state where a medical device such as a suture needle is connected to the tip of the medical suture 100. The operator can also form the extension cover layer 112 and the outer line cover layer 122 for the medical suture 100 on which the extension cover layer 112 and the outer line cover layer 122 are not formed, respectively.

Specifically, the operator processes the wire rod 111a using the twisting machine (not shown) to form the core yarn 110, and then uses the knitting machine (not shown) to use the wire rod 121a on the outer peripheral portion of the core yarn 110. The ultrafine thread 121 is knitted to form the medical suture 100 (that is, a semi-finished product of the medical suture 100). Next, the operator immerses the semi-finished medical suture 100 in a solution containing MPC. In this case, the operator sufficiently infiltrates the solution into each of the ultrafine threads 111 (wire rod 111a) constituting the core thread 110 in the medical suture thread 100.

In this case, the operator can sufficiently change the tension applied to the medical suture 100 of the semi-finished product in the solution containing MPC to sufficiently reach each ultrafine thread 111 (wire material 111a) constituting the core thread 110. The solution can be impregnated. As a result, the operator can obtain the medical suture thread 100 composed of the ultrafine threads 111 and 121 in which the extension cover layer 112 and the outer line cover layer 122 are formed on the outer surfaces of the wire rods 111a and 121a, respectively.

(Operation of medical suture 100)
Next, the operation of the medical suture 100 configured as described above will be described. A user such as a doctor connects the medical suture 100 unwound from the package to a medical device (not shown) such as a suture needle to perform medical treatment such as surgery or treatment of an injury. In this case, in the medical suture 100, the extension cover layer 112 and the outer line cover layer 122 formed on the ultrafine threads 111 and 121 are formed with a weight of 0.1% of the total weight of the wire rods 111a and 121a, respectively. Therefore, it is difficult for the medical suture 100 to have a curl, and even if the suture 100 has a curl, it is resolved in a short time and extends linearly. Further, in this case, in the state where the medical suture 100 is wound in an annular shape, it is difficult for the medical sutures 100 adjacent to each other to stick to each other, and the user can easily straighten the medical suture 100. Can be extended to.

In addition, the user performs medical actions such as pulling out the medical suture 100 sutured to the affected part of the patient. In this case, in the medical suture 100, in addition to the outer layer thread 120, an internal line cover layer 112 made of MPC is formed as an outer layer of each ultrafine thread 111 constituting the core thread 110 arranged inside the outer layer thread 120. Therefore, the friction between the ultrafine threads 111 can be suppressed. As a result, the user can easily operate the medical suture 100 because the medical suture 100 is easily bent.

As can be understood from the above operation description, according to the above embodiment, in the medical suture 100, the extension cover layer 112 made of MPC and the cover layer made of outer line cover layer 122 constitute ultrafine threads 111 and 121, respectively. Since the wires are formed with a weight of 0.05% or more and less than 0.3% of the total weight of the wires 111a and 121a, the medical suture 100 contained in the packaging container in an annular shape is less likely to have a curl. The curl can be easily eliminated.

Furthermore, the practice of the present invention is not limited to the above-described embodiment, and various modifications can be made as long as the object of the present invention is not deviated.

For example, in the above embodiment, the extension cover layer 112 and the outside line cover layer 122 are formed with a weight of 0.1% of the total weight of the wire rods 111a and 121a. That is, the extension cover layer 112 and the outside line cover layer 122 correspond to the cover layer according to the present invention. However, according to the experiment of the present inventor, the extension cover layer 112 and the extension cover layer 122 are formed within a weight range of 0.05% or more and less than 0.3% of the total weight of the wire rods 111a and 121a. I just need to be there. In this case, the extension cover layer 112 and the outside line cover layer 122 are formed within a weight range of 0.1% or more and less than 0.3% of the total weight of the wire rods 111a and 121a, thereby forming the extension cover layer 112. The outer wire cover layer 122 can be easily formed as compared with the case where the outer wire cover layer 122 is formed with less than 0.1% of the total weight of the wire rods 111a and 121a.

Further, in the above embodiment, the extension cover layer 112 and the outer line cover layer 122 are formed as a coating film that completely covers the outer surfaces of the wire rods 111a and 121a. However, as shown in FIG. 3, the extension cover layer 112 and the outside line cover layer 122 can be formed in a state where a part of the outer surfaces of the wire rods 111a and 121a is exposed. As a result, the medical suture thread 100 does not need to form the extension cover layer 112 and the extension cover layer 122 on the entire outer surface of the wire rods 111a and 121a, respectively, and the amount of MPC used and the extension cover layer 112 and the outer line cover layer The work load for forming the 122 can be reduced, and the extension cover layer 112 and the outside line cover layer 122 can be efficiently formed.

Further, in the above embodiment, in the medical suture thread 100, the extension line cover layer 112 and the outer line cover layer 122 are formed on the ultrafine threads 111 and 121 constituting the core thread 110 and the outer layer thread 120, respectively. However, the medical suture 100 may be configured by forming the extension cover layer 112 or the outer line cover layer 122 on the extra-fine thread 111 or the extra-fine thread 121 constituting one of the core thread 110 and the outer layer thread 120.

In this case, the medical suture 100 forms the outer line cover layer 122 only on the outer layer thread 120 or only on the outer layer thread 120 exposed on the outer surface of the medical suture 100, thereby improving the operability of suturing and sliding the suture portion. It is possible to easily eliminate the curl that is difficult to be attached to the medical suture 100 or the curl that is attached to the medical suture 100 while improving the mobility or the slipperiness.

Further, in the above embodiment, the medical suture 100 has the same thickness as the extension cover layer 112 of the ultrafine thread 111 constituting the core thread 110 and the outer line cover layer 122 of the ultrafine thread 121 constituting the outer layer thread 120. (Weight of 0.1% of the total weight of the ultrafine yarns 111 and 121). However, the extension cover layer 112 and the outside line cover layer 122 can be formed to have different thicknesses from each other.

Therefore, for example, the extension cover layer 112 is formed thinner than the outer line cover layer 122 to suppress an increase in the outer diameter of the medical suture 100 and improve the flexibility of the entire medical suture 100, which is good. Operability can be ensured. Further, by forming the extension cover layer 112 thicker than the outer line cover layer 122, it is possible to suppress the disappearance of the extension cover layer 112 due to wear and maintain the flexibility for a long period of time.

Further, in the above embodiment, the core yarn 110 is configured by twisting a plurality of ultrafine yarns 111. Specifically, the core yarn 110 is formed by twisting two bundles of a plurality of ultrafine yarns 111. However, the core yarn 110 can also be formed by twisting three or more bundles. Further, the core yarn 110 can be configured by knitting a plurality of bundles composed of a plurality of ultrafine yarns 111, and can also be configured by arranging a plurality of ultrafine yarns 111 linearly in parallel with each other. Further, the core thread 110 may be composed of one extra-fine thread 111.

Further, in the above embodiment, the outer layer yarn 120 is configured by knitting a plurality of ultrafine yarns 121. Specifically, the outer layer yarn 120 is constructed by knitting five bundles of a plurality of ultrafine yarns 121. However, the outer layer yarn 120 can also be formed by knitting four or less or six or more bundles. Further, the outer layer yarn 120 can also be formed by twisting a plurality of bundles composed of a plurality of ultrafine yarns 121.

Further, in the above embodiment, the medical suture thread 100 is configured by forming an outer layer thread 120 on the outside of the core thread 110. However, the medical suture 100 may be composed of one or a plurality of fibrous ultrafine threads. Therefore, the medical suture 100 may be composed of only one ultrafine thread 111 or ultrafine thread 121.

100 ... Medical suture,
110 ... core thread, 111 ... extra fine thread, 111a ... wire rod, 112 ... extension cover layer,
120 ... outer layer yarn, 121 ... extra fine yarn, 121a ... wire rod, 122 ... outer wire cover layer.

Claims (3)

A medical suture in which one thread is composed of one or more fibrous ultrafine threads.
The extra-fine thread is
A cover layer made of 2-methacryloyloxyethyl phosphorylcholine (MPC) is formed on the outer surface.
The cover layer is
With a weight of 0.05% or more and less than 0.3% of the total weight of the wire rod constituting the ultrafine yarn and forming the cover layer , and with a part of the outer surface of the wire rod exposed. A medical suture that is formed so as to cover 50% or more of the surface area of the wire with uniform formation densities in the axial direction and the circumferential direction of the wire. A medical suture in which one thread is composed of one or more fibrous ultrafine threads.
The extra-fine thread is
A cover layer made of 2-methacryloyloxyethyl phosphorylcholine (MPC) is formed on the outer surface.
The cover layer is
It is formed with a weight of 0.05% or more and less than 0.3% of the total weight of the wire rod constituting the ultrafine yarn and forming the cover layer, and completely covering the outer surface of the wire rod. A medical suture characterized by being In the medical suture according to claim 1 or 2.
The cover layer is
A medical suture that is formed with a weight of 0.1% or more and less than 0.3% of the total weight of the wire rod that constitutes the ultrafine thread and forms the cover layer.

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